Aleksandro Ferreira da Silva

Symbiotic and agronomic efficiency of new cowpea rhizobia from Brazilian Semi-Arid

Cowpea is a very important crop to Brazilian Semi-Arid mainly small family-based farmers. Rhizobia inoculation is a practice, easy to use, and cheap technology that increases cowpea productivity. The aim of this study was to evaluate the efficiency of two new rhizobia isolates in greenhouse and field as well as classify them taxonomically. To bacterial identification the 16S rRNA gene of ESA 17 and ESA 18 isolates were sequenced. The greenhouse test was conducted with pots containing 3 L of soil and the bacterial isolates evaluated were ESA 17, ESA 18,BR 3267 or BR 3262 strains. A field experiment was implemented on a Vertisol in Juazeiro, Bahia State, to evaluate the cowpea growth and productivity. In this experiment, the peat-based inoculants with ESA 17, ESA 18, BR 3267 or UFLA 3-84 were used in 2 cowpea cultivars. Both bacteria were identified as Bradyrhizobium, but related to different species. ESA 17 was related to B. japonicumand ESA 18 was closer to B. pachyrhizi. At greenhouse, both isolates increased cowpea nitrogen content in the shoots due to the presence of very efficient nodules. In the field, the isolate ESA 18 inoculated at BRS Pujante cultivar induced higher production than observed for the absolute control, and for BR 17 Gurgueia cultivar, he ESA 17 and BR 3267 stood out both by inducing high production and grain protein content. The results indicate that both isolates can be evaluated in network experiments aiming at official recommendation for new bacteria to cowpea inoculant in Brazil.

Phenotypic, genetic and symbiotic characterization of Erythrina velutina rhizobia from Caatinga dry forest.

Erythrina velutina (“mulungu”) is a legume tree from Caatinga that associates with rhizobia but the diversity and symbiotic ability of “mulungu” rhizobia are poorly understood. The aim of this study was to characterize “mulungu” rhizobia from Caatinga. Bacteria were obteined from Serra Talhada and Caruaru in Caatinga under natural regeneration. The bacteria were evaluated to the amplification of nifH and nodC and to metabolic characteristics. Ten selected bacteria identified by 16S rRNA sequences. They were tested in vitro to NaCl and temperature tolerance, auxin production and calcium phosphate solubilization. The symbiotic ability were assessed in an greenhouse experiment. A total of 32 bacteria were obtained and 17 amplified both symbiotic genes. The bacteria showed a high variable metabolic profile. Bradyrhizobium (6), Rhizobium (3) and Paraburkholderia (1) were identified, differing from their geographic origin. The isolates grew up to 45 °C to 0.51 mol L−1 of NaCl. Bacteria which produced more auxin in the medium with l-tryptophan and two Rhizobium and one Bradyrhizobium were phosphate solubilizers. All bacteria nodulated and ESA 90 (Rhizobium sp.) plus ESA 96 (Paraburkholderia sp.) were more efficient symbiotically. Diverse and efficient rhizobia inhabit the soils of Caatinga dry forests, with the bacterial differentiation by the sampling sites.

Symbiotic efficiency of native rhizobia in legume tree Leucaena leucocephala derived from several soil classes of Brazilian Northeast region

The effective symbiotic activity of rhizobia can contribute increment of biological nitrogen fixation (BNF), which is of great importance in low technology regions. This study aimed to evaluate the symbiotic efficiency of native rhizobia from Brazilian Northeast soils for selection of the most efficient and competitive strains for Leucaena leucocephala plant. The greenhouse test was conducted in factorial scheme (7x3), with seven fertilization treatments and three soil classes (Luvisol, Ultisol and Oxisol). The fertilization treatments were: (a) four native rhizobia isolates, obtained from nodules of L. leucocephala grown in Brazilian semiarid soils; (b) recommended strain (SEMIA 6069); (c) control without rhizobia inoculation and without N fertilization; (d) control without rhizobia, but with N fertilization (100 mg kg -1 ). The plants were harvested at 90 days and the following characteristics were determined: plant height, diameter, shoots dry matter, roots dry matter and nodules dry matter, number of nodules, nitrogen concentration and accumulation in shoots, and efficiency of nitrogen fixation. The isolates 36F and 45G are very promising on Biologic Nitrogen Fixation (BNF). They showed high symbiotic efficiency (higher than 90%). These selected strains provided the best characteristics such as plant height (57 and 52 cm), diameter (4.03 and 4.02 mm), dry matter of shoot (3.2 and 3.6 g plant -1 ) and nitrogen accumulation in shoots (60 and 65 mg plant-1).